Seems you are having a lot of fun there.... Upgrading the original 2001 first prototype after 13 years of service.

Thats great!

The bottom bearing does not need a seat / support and was self aligning.Once the driveset is in position and running smooth, you can add a drop of loctite thread locker to the edge of a bearing andthe bottom plate - if wished.

BTW, check the backlash on your delrin nuts - trapezium screws, do minimize that with the setscrews and it will work as new.